Visible photoluminescence from Ge nanoclusters implanted in nanoporous aluminum oxide films

Nanoporous aluminum oxide (Al2O3) films with uniform porous size of 45 nm prepared by the electrochemical process in inorganic acid medium were implanted at room temperature (RT) with 120 keV Ge+ ions with a fluence of 1.2 X 10(16) cm(-2). The nucleation and growths of Ge nanoparticles, were obtained by thermal annealing of the implanted samples at the temperature range of 200-600 degrees C. The size and distribution of the nanoparticles were characterized by photoluminescence (PL) measurements. The photoluminescence measurements as a function of the annealing temperature shows that at low annealing temperature (200 degrees C), the sample presents a low intensity and broad emission band centered at 5456 angstrom consistent with emission band characteristies of nanocluster of Ge with diameter in the range of 4-8 nm, as the annealing temperature increases to 400 degrees C the PL intensity increases by a factor of almost 20 and the emission band suffers a small red shift. The intensity increases can be related to the increase of the number of Ge nanocluster. At the annealing temperature of 600 degrees C, the emission band is considerably red shifted by almost 172 angstrom and the emission intensity decreases significantly, strongly suggesting that nanocrystalline Ge having a character of direct optical transitions exhibits the visible photoluminescence. (c) 2005 Published by Elsevier Ltd.